1. Field of the Invention
The present invention relates to the field of virology. In general, the present invention discloses method(s) of treating infection by members of the filovirus family of viruses by directly inhibiting virus entry into the cells or by preventing envelope protein induced toxicity. More specifically, the present invention discloses methods of treating infection by filovirus such as Ebola virus, Marburg virus and related viruses by blocking the PI3 kinase signaling pathway or the calcium-associated signaling pathway.
2. Description of the Related Art
Ebola virus is a member of the family Filoviridae and causes severe hemorrhagic fevers in humans and nonhuman primates. It is an emerging virus and outbreaks have been reported periodically at 2-10 year intervals since its initial identification in 1976. It is a NIH category A agent and is one of the most widely publicized human viruses. Most outbreaks have occurred in isolated communities in Africa and so have been effectively contained. Release into a large city community would likely have severe consequences not only for those infected but as a result of mass panic and major economic disruption. For these reasons Ebola virus remains one of the most highly effective terrorist bioweapon threats.
In the wild, infections initiate from contact of people with dead or dying virus-infected forest animals such as chimpanzees, forest antelope and porcupines that have been regularly found on the rainforest floor in affected areas (World Health Organization, 2004). However, these are dead-end hosts and the primary animal reservoir remains unknown.
The Ebola virus genus includes four subtypes: Zaire, Sudan, Ivory Coast and Reston. The Zaire strain is the most often associated with outbreaks with very high mortality rates, on average between 80 to 90% (Sadek et al., 1995; Peters, 1996, Peters and LeDuc, 1999; Feldman et al., 1993; Baize et al., 1999; Fisher-Hoch and McCormick, 1999). Virus is spread by contact with blood or body fluids from infected individuals or animals and is highly infectious. The final stages of Ebola virus infection are characterized by fever, hemorrhage, hypotensive shock with an apparent dependence on the reticuloendothelial and mononuclear phagocytic cell systems (Peters and LeDuc, 1999; Baskerville et al., 1978; Baskerville et al., 1985; Feldmann et al., 1996; Schnittler and Feldmann, 1999).
Apart from palliative treatment, there is no effective treatment for an Ebola virus infection. Some success has been found using monoclonal antibodies against envelope proteins and nucleoproteins or using passive transfer of immune serum from convalescent patients (Mupapa et al., 1999; Xu et al., 1998) but this is not practical in the situation of a virus outbreak. Patients that survive typically have more rapid Ebola virus-specific humoral and cellular responses than those that die. Therefore delaying virus spread would give a greater opportunity for the immune system to mount an effective anti-viral response. Then drugs that can prevent or slow an ongoing infection would likely be effective in treatment.
Previous research has suggested that mononuclear phagocytic cells and endothelial cells are sites of Ebola virus replication early in infection although evidence of replication has been observed in many tissues including the liver, spleen and lymph nodes (Connolly et al., 1999; Geisbert et al., 2000; Nabel, 1999; Schnittler et al., 1993; Yang et al., 1998). The pantropic nature of Ebola virus infection suggests a role for monocytes in disseminating the virus to distant sites (Schnittler and Feldmann, 1999; Schnittler and Feldmann, 1998; Stroher et al., 2001). It has been hypothesized that cytokines released from infected mononuclear cells contribute highly to the hypotensive shock and cell damage seen during the later course of infection (Schnittler and Feldmann, 1999; Stroher et al., 2001). Apoptosis is also seen in endothelial cells from fatally infected patients (Baize et al., 1999). There are probably numerous factors involved in the effects seen during Ebola virus infections including virus induced cytokine production that alters vascular permeability, as well as other yet to be identified factors. Identification of these factors is important for the discovery of drugs that can prevent and treat infection and is a major goal of this proposal.
The Ebola virus envelope glycoprotein (GP) determines the cell binding and entry properties of the virus. Ebola virus glycoprotein contains both the receptor-binding domain and fusion mechanism of the virus and is the primary target of a neutralizing antibody response. It is the first virus protein that makes contact with cells and may induce cell-signaling pathways that allow establishment of infection. Ebola virus glycoprotein has also been identified as a major viral determinant of vascular cell cytotoxicity, permeability and injury (Yang et al., 2000). When Ebola virus glycoprotein was expressed at levels comparable to those seen in an in vivo infection, cell death resulted in a variety of cell types. Treatment of cells with Ebola virus envelope protein also resulted in rounding and detachment in culture (Simmons e al., 2002). In rapid entry assays, it was observed that Ebola virus takes a long time (4 h) to penetrate cells compared to other viruses like Murine leukemia virus (20 min) or Vesicular stomatitis virus. These observations suggest that Ebola virus primes or triggers the cell for entry to take place. While it is unlikely that Ebola virus glycoprotein cytotoxicity is solely responsible for the pantropic destruction seen in Ebola virus-induced hemorrhagic fever, this protein is still a major and accessible virulence factor that requires further study.
Thus, prior art is deficient in methods to treat individuals infected with filoviruses. The present invention fulfills this long-standing need and desire in the art.